Plant growth promoting rhizobacteria are more effective under drought: a meta-analysis

Abstract

Plant growth promoting rhizobacteria (PGPR) have been shown to reduce abiotic stress on plants, but these effects have not been quantitatively synthesized. We evaluated the degree to which plant growth promoting rhizobacteria (PGPR) improve plant performance with and without drought stress. We used meta-analysis to summarize 52 published articles on the effects of PGPR on root mass, shoot mass and yield under well-watered and drought conditions. We also asked whether fertilization treatments, experimental conditions, inoculum taxonomic complexity, plant functional group, or inoculum delivery method introduce variation in the effect size of PGPR. Across all treatments, plants were highly responsive to PGPR; under well-watered conditions, root mass increased by 35%, shoot mass increased by 28%, and reproductive yield increased by 19%. Under drought conditions, the effect was even higher: root mass increased by 43%, shoot mass increased by 45%, and reproductive yield increased by 40%. The effect of PGPR was significantly larger under drought for shoot mass (p < 0.05) and reproductive yield (p < 0.05), but not for root mass. PGPR responsiveness also varied according to plant functional group, with C3 grass shoot production responding the least strongly to PGPR. We demonstrate that PGPR are highly effective for improving plant growth, with a greater effect under drought for above ground traits. While previously known for their bio-control abilities, we show that PGPR may also contribute to drought amelioration and water conservation.